This organization of specific DNA sequences in the budding yeast, Saccharomyces cerevisiae, has been pursued by the analysis of recombinant DNA molecules containing yeast DNA. The analysis of a large number of ribosomal DNA-containing molecules established the nature and linkage of ribosomal DNA in this organism. A putative histone DNA-containing clone was identified by colony hybridization with sea urchin histone DNA. This yeast recombinant DNA molecule is currently under investigation to further characterize the nature of the mRNA which is complementary to it. Recombinant DNA molecules which contain abundant mRNA sequences have been identified and are currently being characterized. Finally, a scheme has been devised to enrich for ribosomal protein mRNA. This enriched population of mRNA will be used to identify "candidate" molecules which contain ribosomal protein mRNA sequences.